a Synchronism check relay

[bejoyengineer]

I am not sure how a Synchronism check relay works? Any good sites with explanations would be of great help?.. As the name and description given in manuals, it states that this relay checks the voltage, magnitude, phase angle and frequency between the lines connected to the in and out of a breaker that is ready for a close operation or in other words it checks the voltages between the incoming line (line going to the breaker) and the bus( the part that is going out of the breaker and connected to the bus). But in the actual case ?only the incoming line to the breaker will be hot and the outgoing line from the breaker to bus will not be hot and will become hot only if we close the breaker. So in that case ? how will it actually compare the voltage, magnitude, phase angle and frequency as we have a live line and a dead bus condition all the time and there by closing the breaker? When and Where does the comparison take place?

 

[bob]

Google Synchronism check relay . Lots of hits.

 

[ron]

Normally a synch check relay to to ensure sync between the line and load, or two sources before performing a function.
If the line side is hot and the load side is always de-energized until the breaker closes, why do you need a synch check?

 

[Besoeker]

Normally a synch check relay to to ensure sync between the line and load, or two sources before performing a function.
If the line side is hot and the load side is always de-energized until the breaker closes, why do you need a synch check?

I have mostly seen them used to ensure synchronisation (in voltage frequency, and phasing) before closing an alternator on to the grid.

 

[don_resqcapt19]

I have mostly seen them used to ensure synchronisation (in voltage frequency, and phasing) before closing an alternator on to the grid.

In that case you are comparing two energized circuits, not one energized and one dead.

 

[LRB]

Sync Check Relay

Sync Check Relay

I have only seen them used to check two sources of power before tieing them together, so yes there is power on both sides of the open breaker. When closing onto a dead buss the sync-check is deactvated either manually or automaticly

 

[nawao]

A dead bus relay override the functions of the check sync relay to allow closure on a dead bus

 

[Besoeker]

In that case you are comparing two energized circuits, not one energized and one dead.

That was my point.
Its purpose is to synchronise two energised circuits.
There is nothing to synchronise if one circuit is dead.

 

[nawao]

The first generator closes its breaker to a dead bus in an islanded system. The dead bus relay override the check sync relay to allow breaker closuree. The following generators will syncronize before closing their breakers. In other words, allways the first generator closes to dead bus.

 

[beanland]

Synch Check

Synch Check

Synch Check looks at voltage, frequency, and phase angle across an open breaker. The synch check blocks the breaker from closing if there is too much difference either in voltage, frequency, or phase angle. Once the angle is within a set range (e.g. +/- 30 degrees), the relay allows the breaker to close. This is done to minimise the mechanical torsional loads and electrical surges of closing a breaker between two un-synchronized power sources.

 

[Besoeker]

The first generator closes its breaker to a dead bus in an islanded system. The dead bus relay override the check sync relay to allow breaker closuree. The following generators will syncronize before closing their breakers. In other words, allways the first generator closes to dead bus.

You have a similar situation with a "black start".
Nothing with which to power the alternator excitation and nothing to synchronise with.